Developmental delay, while multifactorial, is increasingly seen as mediated by suboptimal "proximal factors" in the home caregiving environment. Delays pose a major public health problem. Preventive early intervention programs can improve both proximal factors and child outcomes but it has been difficult to disentangle the contribution of parent-focused and direct child components. Addressing the need of Part C programs like the Infant Child Health Assessment Program (ICHAP) to provide targeted cost-effective preventive services to at-risk 0- 3-yr.-old children and their families, the project proposes a randomized controlled trial (RCT) to assess the impact of a low- intensity preventive intervention focused entirely on proximal factors in the home. In the proposed intervention, ICHAP regularly mails the family Ages and Stages Questionnaires (ASQs - parent-completed developmental questionnaires) together with monthly Building Blocks (age-paced newsletters with parenting and developmental guidance) and a corresponding toy. The intervention involves a partnership and dynamic interaction between the family, the child's primary care provider (PCP) who introduces and reinforces the approach, and ICHAP. In the RCT, families with 4-7-month-old infants attending one of two sites serving poor Black and Hispanic communities will be offered enrollment by their PCP. Those who accept will be randomized to: A) a control group who receive conventional provider-based screening only, and B) the ASQ/BB intervention group. At 12, 24, and 36 months of age, the families will be assessed on proximal factor measures of the home environment, parenting style and parent-child interaction. Additionally the Bayley will be administered to the child. The project will examine whether, over time, the intervention has a significant impact on Bayley scores, and the degree to which this effect is mediated by improvements in proximal home factors. Additionally, the degree that the severity of psychosocial and biomedical risk factors, race/ethnicity, acculturation and health status modify the effect will be studied to identify the population subgroups most amenable to the intervention.